Bendable, Self-Healing Concrete

Concrete that heals itself has been developed at the University of Michigan. The engineered cement composite is designed to bend; it cracks in narrow hairlines rather than in wide gaps, as does standard concrete. The material was developed in the lab of Victor Li, the E. Benjamin Wylie Collegiate Professor of Civil Engineering and a professor of Materials Science and Engineering.

The engineers found that cracks must be kept below 150 micrometers, and preferably below 50, for full healing...

More flexible than traditional concrete, ECC acts more like metal than glass. Traditional concrete is considered a ceramic. Brittle and rigid, it can suffer catastrophic failure when strained in an earthquake or by routine overuse, Li said. But flexible ECC bends without breaking. It is studded with specially-coated reinforcing fibers that hold it together. ECC remains intact and safe to use at tensile strains up to 5 percent. Traditional concrete fractures and canít carry a load at .01 percent tensile strain.

The average crack width in [the] self-healing concrete is below 60 micrometers. Thatís about half the width of a human hair. His recipe ensures that extra dry cement in the concrete exposed on the crack surfaces can react with water and carbon dioxide to heal and form a thin white scar of calcium carbonate. Calcium carbonate is a strong compound found naturally in seashells. In the lab, the material requires between one and five cycles of wetting and drying to heal.

The first time I read about the idea of a bendable, self-healing material was in the work of science fiction writer J.G. Ballard. In his 1962 short story The Thousand Dreams of Stellavista, he wrote about psychotropic houses with bendable walls that responded to the emotions of visitors. The walls were made of plastex.

It was a beautiful room all right, with opaque plastex walls and white fluo-glass ceiling, but something terrible had happened there. As it responded to me, the ceiling lifting slightly and the walls growing less opaque, reflecting my perspective-seeking eye, I noticed that curious mottled knots were forming, indicating where the room had been strained and healed faultily.
(Read more about plastex)

Update 28-Apr-2012: In his 1951 novel Asteroid of Fear, Raymond Z. Gallun wrote about self-sealing plastic that was used in space to protect against damage by micrometeorites.

...It even had an inter-skin layer of gum that could seal the punctures that grain-of-sand-sized meteors might make.

End update.

If the idea of a self-healing house or structure appeals to you, read about an entirely different approach taken in Nanotech Self-Healing Houses .